Molecular scanner

ABSTRACT

A device and method in which neutral atoms or molecules are used to observe surfaces of samples and capable in particular of producing information from inhomogeneous samples where the forces and interactions are of strength characterized by moderate temperatures in the range of 100*K to 500*K. Molecules evaporating from the surface of a sample are shown selected by a pin-hole and detected and converted to an ion current by a surface ionizing detector. With relative scanning movement of components of the system, the ion current is monitored and recorded, indicating the spatial variation in evaporation of the molecules from the sample.

United States Patent [191 King Feb. 5, 1974 MOLECULAR SCANNER [75]Inventor: John G. King, Brookline, Mass.

[73] Assignee: Massachusetts Institute of Technology, Cambridge, Mass.

[22] Filed: Nov. 5, 1971 [21] Appl. N0.: 196,236

Related US. Application Data [63] Continuation of Ser. No. 56,056, June25, 1970, abandoned, which is a continuation of Ser. No. 713,969, March18, 1968, abandoned.

[52] US. Cl 250/251, 250/306, 250/307, 250/389, 250/423, 250/493 [51]Int. Cl G0ln 27/78, l-lOls H00 [58] Field of Search, 250/413, 41.9 SE,42, 49.5 R, 250/495 E, 49.5 P, 84

[56] References Cited UNITED STATES PATENTS 3,180,987 4/1965 Cunninghamet al 250/495 3,415,985 12/1968 Castaing et al. 250/495 OTHERPUBLICATIONS Abbildung Von Verdampfungsquellen Mit DemLochkamerauerfahren by H. Boersch et al. from Zeitschrift Fur Physik,Vol. 139, N0. 3, 1954, pgs. 243-250.

Some New Applications and Techniques of Molecular Beams by J. G. King etal. from Advances in Electronics and Electron Physics, Vol. 8, 1956,pgs. 42-51.

Strong Ion Source For Ions From Solids by E. F. Krimmel from The Reviewof Scientific Instruments, Vol. 37, No. 5, May, 1966, pgs. 678 & 679.

Primary Examiner-William F. Lindquist Attorney, Agent, or Firm-Arthur A.Smith, Jr.; Martin M. Santa; John N. Williams [57] ABSTRACT A device andmethod in which neutral atoms or molecules are used to observe surfacesof samples and capable in particular of producing information frominhomogeneous samples where the forces and interactions are of strengthcharacterized by moderate temperatures in the range of 100K to 500K.Molecules evaporating from the surface of a sample are shown selected bya pin-hole and detected and converted to an ion current by a surfaceionizing detector. With relative scanning movement of components of thesystem, the ion current is monitored and recorded, indicating thespatial variation in evaporation of the molecules from the sample.

19 Claims, 5 Drawing Figures ELECTRO METER 1 VACUUM I PUMP {r I VACUUMPUMP CURRENT SOURCE mimenm 5:914

sum 1 or 2 ELECTRO METER VACUUM PUMP PUMP VACUUM INVI NTUH' J (1 KINGATTORNEY Pmmmrm sasm 3,790,793

SHEEI 2 {1F 2 FIG. 3

INVENTOR J.G. KING ATTORNEY MOLECULAR SCANNER This application is acontinuation of my co-pending application Ser. No. 56,056 filed June 25,1970, now abandoned, which in turn is a continuation of my copendingapplication Ser. No. 713,969, filed Mar. 18, 1968, now abandoned.

The invention herein described was made in the course of a contractsponsored by the United States Army Electronics Command.

This invention relates to scanning devices and in particular to devicesfor viewing matter by means of beams of molecules.

In accordance with this invention, a visible image that represents thespatial distribution of neutral molecule emissions from a sample, inwhich molecules are defined as comprising electrically neutal materialparticles of low energy, is formed. Molecules are emitted from a sampleand passed through a pinhole to strike a plate where they are read outby an electron beam that desorbs and ionizes the molecules. The desorbedions are focussed by ion lenses to strike a fluorescent screen which canbe photographed or observed with the eye. In this way, neutral moleculescan be used to study, for example, the diffusion and evaporation ofalkali atoms or alkali oxide molecules along grain boundaries in asample.

The device utilizes the concept of observing matter by means of neutralatoms instead of by particles of essentially electromagnetic origin. Theinteraction is that of the electric and magnetic multipoles of theincident atoms and the corresponding electric and magnetic fielddistributions in the sample. Thus one obtains an entirely different viewof matter than that which is obtained with either light, electrons, orions, a view of matter which is appropriate to problems of metallurgy,chemistry, and biology where the forces and interactions are of strengthcharacterized by moderate temperatures in the range of ll( to 500K.

It is the object of this invention to determine the spatial variation inevaporation of neutral atoms or mole cules from an inhomogeneous sample.

It is a further object of this invention to form a visible image thatrepresents the spatial distribution of neutral molecule emissions fromthe sample.

Other objects, advantages, and novel features of the invention willbecome apparent from the following detailed description thereof whenconsidered in conjunction with the accompanying drawing in which likenumerals represent like parts throughout and wherein:

FIG. 1 illustrates one embodiment of the invention;

FIG. 2(a) shows the detector current as the detector is traversed acrossthe sample;

FIG. 2(b) shows representative molecular beam trajectories and asectional view of the sample along line A-A in FIG. 2(c);

FIG. 2(c) is a top view of the sample;

FIG. 3 illustrates an alternative embodiment of the invention.

Referring to FIG. 1, the device consists of a vacuum envelope 1connected to vacuum pumps 18 by pipes 2. The device is divided into twochambers by a septum 3 equipped with a small aperture 4, the size of apinhole. The lower chamber, which is the sample chamber, is equippedwith water-cooled electrodes 5 which carry heating current from currentsource 20 into a crucible 6 preferably made of platinum. The sample 7,

which consists of a piece of fused potassium feldspar 14 containingquartz grains 15, is placed in the crucible 6 and heated to atemperature sufficient to evaporate molecules from the feldspar 14 butnot the quartz 15. 1,200C was determined to be a suitable temperaturefor evaporating the atoms or molecules. Molecules evaporating fromvarious parts of the sample 7 pass through the aperture 4 and strike amovable surface ionizing detector consisting of a hot platinum wire 9having a sharp, V-shaped point, a collector electrode 8 having anopening for passage of the molecules, and an insulator 16, preferablymade of boron nitride, rigidly connected between the wire 9 andelectrode 8. A description of the surface ionizing detector is given inAdvances in Electronics and Electron Physics (Vol. VIII, page 42, 1956),by John G. King and Jerrold R. Zacharias. The platinum wire 9 is heatedby a current passing through the leads l1. Molecules striking the pointof the wire 9 are ionized and collected by the electrode 8 as an ioncurrent 17 proportional to the number of neutral atoms per secondstriking the wire 9. The ion current 17 is monitored by means of lead 12insulated by an insulator 13. Varying the pressure produces expansion orcontraction of the bellows 10, which is connected to the insulator 16 toimpart to the detector motion in parallel with the septum 3, therebycausing the detector to traverse across the septum. The resultant ioncurrent 17 shown in FIG. 2(a), suitably amplified by an electrometer 19,is recorded, representing a single line scan of the sample 7. By alsoscanning in a direction transverse to the septum 3, an image of theevaporating sample could be mapped. Increased magnification of thedevice can be obtained by increasing the ratio of the distance betweenthe aperture 4 and the electrode 8 to the distance between the aperture4 and the sample 7. Magnifications of should be readily available bysuch techniques.

FIGS. 2(a), 2(b), and 2(0) should be viewed together. FIG. 2(c) showsthe general appearance of the sample 7, and, in particular, three quartzgrains 15 which the detector will scan. FIG. 2(b) shows representativemolecular beam trajectories. Note that as the detector traverses acrossthe sample 7 the quartz grains l5 block out the beams with a resultantabsence of ion current 17 as shown in FIG. 2(a); in like manner, themolecular beams resulting from evaporation of the feldspar 14 passthrough the aperture 4 and are represented by the corresponding ioncurrent as shown in FIG. 2(a). FIG. 2(a), therefore, represents thespatial variation in evaporation from the inhomogeneous sample 7 asobserved by means of the neutral molecules.

Alternatively, it would be possible to study grain boundary diffusion inmetals by using sharp-point, field ionizing detectors capable ofionizing all atoms in lieu of surface ionizing detectors and massspectrometers to determine what species of atom are involved.

In accordance with one concept of the above embodiment, besidesobserving molecules from desorbing or outgassing surfaces, one couldbombard the surface with charged particles and examine the ejectedneutral molecules or expose the surface to beams of neutral molecules,possibly selected according to electric or magnetic sub-states andpossible velocity selected, and examine the scattered beams. Variousproperties of the sample could be studied by varying both itstemperature and that of the incident beam.

In another embodiment of the invention shown in FIG. 3 in which thesample 7 in high vacuum emits a beam 28 of neutral molecules, themolecules moving in the appropriate direction are allowed to passthrough a pinhole 21 to strike a plate 22 maintained at low temperaturesby means of a coolant 23, so that the molecules deposit on the plate 22having a grid 29 in a distribution which forms an image of the emittersample 7. The molecules in the image 30 are read out by means of anarrow scanning electron beam 24 generated by an electron gun 31 havingdeflection plates 32 that simultaneously desorbs and ionizes themolecules. The desorbed ions 25 are then magnified and focussed by ionlenses 26 so as to strike a fluorescent screen 27 which can bephotographed or observed with the eye. Thus, a visible imagerepresenting the spatial distribution of neutral molecule emission fromthe sample 7 is formed.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is, therefore, tobe understood that within the scope of the appended claims the inventionmay be practiced other than as specifically described.

What is claimed is:

1. Apparatus for forming a visible image representing the spatialdistribution of neutral molecular emission from a sample comprising:

a. means for maintaining the sample in a vacuum:

b. means for emitting only low energy neutral surface molecules fromspecific locations among all the molecules of the sample surface;

c. means for selecting these emitted molecules to provide a magnifiedmolecular spatial distribution representing the locations of eachmolecular emission from the sample;

(1. means for detecting the spatially distributed molecules from alimited region of the sample to provide a spatial distribution of ionsof these molecules; and

e. means for selectively changing the limited region of the sample whichis detected.

2. Apparatus as recited in claim 1, wherein the means for emittingneutral molecules from the sample comprises:

a. a crucible which holds the sample; and

b. water-cooled electrodes capable of carrying heating current connectedto the crucible to heat the sample to a temperature sufficient toevaporate only some of the molecules from the sample.

3. Apparatus as recited in claim 1, wherein the selecting meanscomprises a septum having a first aperture the size of a pinhole locatedbetween the sample and the detecting means to allow emitted molecules topass through the aperture.

4. Apparatus as recited in claim 3, wherein the detecting meanscomprises a surface ionizing detector.

5. Apparatus as recited in claim 4, wherein the surface ionizingdetector comprises;

a. a wire having a sharp, V-shaped point heated to an electron currentso as to ionize molecules striking the point;

b. a collector electrode having a second aperture located between theseptum and the wire, the collector electrode allowing molecules thatpass through the first aperture and the second aperture to strike thepoint, resulting in an ion current flowing in the collector electrodewhich is proportional to the number of neutral molecules per secondstriking the point; and

c. means for moving the collector electrode and wire in fixed relationto one another and in parallel with the septum so that the detectorscans the molecules that pass through the first aperture, said lastnamed means serving as said means for selectively changing the limitedregion of the sample which is detected.

6. Apparatus as recited in claim 5, wherein the moving means comprises:

a. a bellows;

b. an insulator rigidly connected between the collector electrode andwire; and

c. a control wire connected between the bellows and the insulatorcausing the wire and electrode to move in fixed relation to one anotherand in parallel with the septum when the bellows is expanded orcontracted by a varying pressure.

7. Apparatus as recited in claim 5, including an electrometer connectedto the electrode to amplify the ion current thereby providing arecording that represents the spatial distribution of molecular emissionfrom the sample.

8. Apparatus as recited in claim 1, wherein the detecting means and themeans for selectively changing the limited region of the sample which isdetected include:

a. a plate located along the path of the selected molecules so thatmolecules deposit on the plate;

b. a coolant in thermal contact with the plate to maintain the plate ata temperature sufficient to cause the molecules to remain wheredeposited; and

c. an electron gun having deflection plates so as to direct a scanningelectron beam on the deposited molecules causing the molecules to desorband ionize.

9. Apparatus as recited in claim 8 including:

a. a fluorescent screen; and

b. ion lenses located between said plate and the fluorescent screen soas to focus the ions on the screen thereby forming a visible image ofthe selected molecules.

10. A method for forming a visible image representing the spatialdistribution of neutral molecular emission from a sample comprising:

a. producing a vacuum in a chamber containing said sample;

b. heating said sample to cause emission of low energy molecules fromspecific regions only of the sample surface;

c. selecting those emitted molecules which originate over only a smallregion of the surface;

d. with a detecting means detecting these selected emitted molecules;

e. selecting different regions of the surface and detecting moleculesemitted from these different regions; whereby a magnified representationof the molecular distribution on the surface is obtained.

11. The method of claim 10 wherein said selecting of molecules fromdifferent regions of the surface is accomplished by causing relativemovement between the detecting means and the sample.

12. The method of claim 10 wherein said selecting of molecules fromdifferent regions of the surface is accomplished by causing relativemovement between the detecting means and a pin hole means, said pin holemeans performing the function of selection of molecules which originateover only a small region of the surface.

13. A device for analyzing an inhomogeneous sample, capable of producinginformation concerning constituents at the surface of the sample incases where the forces and interactions are of strength characterized bytemperatures in the range of 100K to 500K, said device comprising thecombination of means for causing neutral molecules to be emitted from asample, means defining a pinhole positioned to transmit a beam of saidneutral molecules as they proceed from the sample, and an electricaldetector having a narrow effective area relative to the beam ofparticles at the region of detection, a scanning drive for effectivelyproducing relative scanning motion between said sample, pinhole, anddetector thereby to progressively ionize said molecules and produce anelectrical signal representing the spatial distribution of neutralmolecules from the sample.

14. The device of claim 13 including a plate aligned with said beam toproduce a deposit of molecules from said pinhole thereupon and means toproduce said scanning motion of said detector relative to said plate.

15. The device of claim 14 wherein said detector comprises an ionizingbeam device directed to scan said plate and an ion detector for ionsdesorbed from said plate.

16. The device of claim 13 wherein said electrical detector is alignedto receive said molecules directly from said pinhole.

17. A method for analyzing an inhomogeneous sample, capable of producinginformation concerning constituents at ,the surface of the sample incases where the forces and interactions are of strength characterized bytemperatures in the range of K to 500K, said method comprising the stepsof causing neutral molecules to be emitted from a sample, providing apinhole positioned to transmit a beam of said neutral molecules as theyproceed from the sample, providing an electrical detector having anarrow effective area relative to the beam of particles at the region ofdetection, and effectively producing relative scanning motion betweensaid sample, pinhole and detector thereby to progressively ionize saidmolecules and produce an electrical signal representing the spatialdistribution of neutral molecules from the sample.

18. The method of claim 17 including maintaining said sample undertemperature and pressure conditions at which certain molecules at saidsurface evaporate and certain different molecules at said surface donot, said method producing information about said first mentionedmolecules.

19. Apparatus for analyzing an inhomogeneous sample, capable ofproducing information concerning constituents at the surface of thesample in cases where the forces and interactions are of strengthcharacterized by temperatures in the range of 100K to 500K comprisingmeans to release surface molecules bound with en ergy up to a certainlevel and not to release surface molecules bound with a certain higherlevel, and an electrical detector adapted to respond effectively to saidreleased molecules, the apparatus including a scanning system whereby,effectively, said molecules are detected from point to point thereby toprogressively produce an electrical representation of the spatialdistribution of said certain surface molecules of the sample.

1. Apparatus for forming a visible image representing the spatialdistribution of neutral molecular emission from a sample comprising: a.means for maintaining the sample in a vacuum: b. means for emitting onlylow energy neutral surface molecules from specific locations among allthe molecules of the sample surface; c. means for selecting theseemitted molecules to provide a magnified molecular spatial distributionrepresenting the locations of each molecular emission from the sample;d. means for detecting the spatially distributed molecules from alimited region of the sample to provide a spatial distribution of ionsof these molecules; and e. means for selectively changing the limitedregion of the sample which is detected.
 2. Apparatus as recited in claim1, wherein the means for emitting neutral molecules from the samplecomprises: a. a crucible which holds the sample; and b. water-cooledelectrodes capable of carrying heating current connected to the crucibleto heat the sample to a temperature sufficient to evaporate only some ofthe molecules from the sample.
 3. Apparatus as recited in claim 1,wherein the selecting means comprises a septum having a first aperturethe size of a pinhole located between the sample and the detecting meansto allow emitted molecules to pass through the aperture.
 4. Apparatus asrecited in claim 3, wherein the detecting means comprises a surfaceionizing detector.
 5. Apparatus as recited in claim 4, wherein thesurface ionizing detector comprises; a. a wire having a sharp, V-shapedpoint heated to an electron current so as to ionize molecules strikingthe point; b. a collector electrode having a second aperture locatedbetween the septum and the wire, the collector electrode allowingmolecules that pass through the first aperture and the second apertureto strike the point, resulting in an ion current flowing in thecollector electrode which is proportional to the number of neutralmolecules per second striking the point; and c. means for moving thecollector electrode and wire in fixed relation to one another and inparallel with the septum so that the detector scans the molecules thatpass through the first aperture, said last named means serving as saidmeans for selectively changing the limited region of the sample which isdetected.
 6. Apparatus as recited in claim 5, wherein the moving meanscomprises: a. a bellows; b. an insulator rigidly connected between thecollector electrode and wire; and c. a control wire connected betweenthe bellows and the insulator causing the wire and electrode to move infixed relation to one another and in parallel with the septum when thebellows is expanded or contracted by a varying pressure.
 7. Apparatus asrecited in claim 5, including an electrometer connected to the electrodeto amplify the ion current thereby providing a recording that representsthe spatial distribution of molecular emission from the sample. 8.Apparatus as recited in claim 1, wherein the detecting means and themeans for selectively changing the limited region of the sample which isdetected include: a. a plate located along the path of the selectedmolecules so that molecules deposit on the plate; b. a coolant inthermal contact with the plate to maintain the plate at a temperaturesufficient to cause the molecules to remain where deposited; and c. anelectron gun having deflection plates so as to direct a scanningelectron beam on the deposited molecules causing the molecules to desorband ionize.
 9. Apparatus as recited in claim 8 including: a. afluorescent screen; and b. ion lenses located between said plate and thefluorescent screen so as to focus the ions on the screen thereby forminga visible image of the selected molecules.
 10. A method for forming avisible image representing the spatial distribution of neutral molecularemission from a sample comprising: a. producing a vacuum in a chambercontaining said sample; b. heating said sample to cause emission of lowenergy molecules from specific regions only of the sample surface; c.selecting those emitted molecules which originate over only a smallregion of the surface; d. with a detecting means detecting theseselected emitted molecules; e. selecting different regions of thesurface and detecting molecules emitted from these different regions;whereby a magnified representation of the molecular distribution on thesurface is obtained.
 11. The method of claim 10 wherein said selectingof molecules from different regions of the surface is accomplished bycausing relative movement between the detecting means and the sample.12. The method of claim 10 wherein said selecting of molecules fromdifferent regions of the surface is accomplished by causing relativemovement between the detecting means and a pin hole means, said pin holemeans performing the function of selection of molecules which originateover only a small region of the surface.
 13. A device for analyzing aninhomogeneous sample, capable of producing information concerningconstituents at the surface of the sample in cases where the forces andinteractions are of strength characterized by temperatures in the rangeof 100*K to 500*K, said device comprising the combination of means forcausing neutral molecules to be emitted from a sample, means defining apinhole positioned to transmit a beam of said neutral molecules as theyproceed from the sample, and an electrical detector having a narroweffective area relative to the beam of particles at the region ofdetection, a scanning drive for effectively producing relative scanningmotion between said sample, pinhole, and detector thereby toprogressively ionize said molecules and produce an electrical signalrepresenting the spatial distribution of neutral molecules from thesample.
 14. The device of claim 13 including a plate aligned with saidbeAm to produce a deposit of molecules from said pinhole thereupon andmeans to produce said scanning motion of said detector relative to saidplate.
 15. The device of claim 14 wherein said detector comprises anionizing beam device directed to scan said plate and an ion detector forions desorbed from said plate.
 16. The device of claim 13 wherein saidelectrical detector is aligned to receive said molecules directly fromsaid pinhole.
 17. A method for analyzing an inhomogeneous sample,capable of producing information concerning constituents at the surfaceof the sample in cases where the forces and interactions are of strengthcharacterized by temperatures in the range of 100*K to 500*K, saidmethod comprising the steps of causing neutral molecules to be emittedfrom a sample, providing a pinhole positioned to transmit a beam of saidneutral molecules as they proceed from the sample, providing anelectrical detector having a narrow effective area relative to the beamof particles at the region of detection, and effectively producingrelative scanning motion between said sample, pinhole and detectorthereby to progressively ionize said molecules and produce an electricalsignal representing the spatial distribution of neutral molecules fromthe sample.
 18. The method of claim 17 including maintaining said sampleunder temperature and pressure conditions at which certain molecules atsaid surface evaporate and certain different molecules at said surfacedo not, said method producing information about said first mentionedmolecules.
 19. Apparatus for analyzing an inhomogeneous sample, capableof producing information concerning constituents at the surface of thesample in cases where the forces and interactions are of strengthcharacterized by temperatures in the range of 100*K to 500*K comprisingmeans to release surface molecules bound with energy up to a certainlevel and not to release surface molecules bound with a certain higherlevel, and an electrical detector adapted to respond effectively to saidreleased molecules, the apparatus including a scanning system whereby,effectively, said molecules are detected from point to point thereby toprogressively produce an electrical representation of the spatialdistribution of said certain surface molecules of the sample.